1. Field of the Invention
This invention relates to a slide block breech mechanism assembly for cannon. This mechanism embodies a multi-lug breech block and breech ring to minimize regions of high firing stresses in each component without increasing the size or weight of the assembly.
2. Description of the Prior Art
Heretofore, when a cannon was designed to enable it to deliver a projectile over a greater distance and, or, to enable a fired projectile to have greater armor penetration, an interrupted slotted screw-type breech mechanism was often used. This type of mechanism had the advantages of strength, reduction of weight in the breech section, uniform distribution of stresses produced by the powder pressure, and adaptability to a method of securing obturation with separately-loaded ammunition.
However, when a rapid fire cannon is required, one usually employs a sliding-wedge type of breech mechanism assembly. This assembly is normally of simple construction and employs a rectangular wedge-shaped block securely seated in a slot in the breech ring, with its longitudinal axis perpendicular to the bore of the cannon tube. However, this assembly must necessarily be of a heavy section to provide the strength necessary to withstand the highly concentrated firing stresses produced therein.
Reliability and durability must be considered to provide a cannon to meet the condition of hard service life with a minimum of down time. Fatigue crack initiation in both the breech ring and the slide block must be minimized to provide a long service life of the breech mechanism assembly. Therefore, it is necessary for the stresses produced in the block during firing to be distributed throughout the entire block as equally as possible. The force or load acting on the block must be transmitted to the breech ring in a manner that minimizes crack initiation in the ring.
A prior art conventional type of slide block breech mechanism comprises a T-shaped slide block. Two oppositely disposed integral lugs have respective bearing surfaces which comprise, in part, the rear surface area of the block. Oppositely disposed integral flanges of the breech ring have bearing surfaces which are in contact with respective bearing surfaces of the lugs when the breech block is in the locked position for firing. The flanges of the ring retain the block within the breech ring during firing of a cannon tube affixed to the forward portion of the ring. The surfaces of the lugs and flanges may be machined in a manner that when the respective bearing surfaces slide over each other, the block is wedged forward to force a cartridge shell into the chamber of the cannon tube. This action also results in a tight fit between the forward face of the block and the breech end of the cannon tube. In a similar manner, the disengagement of the block from the ring will move the block rearward and away from the breech of the tube.
When the cannon is fired, a reactive force resulting from the burning propellant causes the block to move rearward. The force, or load, is immediately transferred to the flanges of the ring by means of the respective pairs of contacting bearing surfaces. The block is slidably mounted in a cavity in the breech ring with very little clearance in order to provide smooth and continuous operation of the block. Only small radius fillets can be provided in areas of high stress concentration.
However, continuous use of the mechanism assembly produces continuous cycling of stress concentration in the small fillets and failure occurs due to metal fatigue thereby prematurely terminating the reliable useful life of the breech ring.
M. A. Lynch, in U.S. Pat. No. 617,110, teaches a breech mechanism for ordnance embodying a plurality of ribs or flanges slidably mounted in the respective grooves of the breech lugs. The bearing contact surface of each rib and the bearing contact surface of its respective groove comprise substantially all of the surface area of the respective lug and groove.
Colonel Thomas J. Hayes in "Elements of Ordnance" copyrighted in 1938 by John Wiley and Son, New York, teaches at page 232, FIG. 4, a similar type of breech mechanism as Lynch.
In all instances, the breech block bearing surface of each rib, flange, or lug is in contact with the respective bearing surface of the breech ring groove, or recess, prior to, and at the moment of firing. When the cannon is fired, the force, or load, acting on the slide block is immediately transmitted to the ring through each contact surface. The force, or load, transmitted produces unequal, and therefore excessive, stress concentrations in both the breech ring and block. Excessive stress concentrations result in premature failure of the breech mechanism.
It is therefore an object of this invention to provide a new and improved slide block breech mechanism which overcomes the deficiencies of the prior art by designing a load distribution which tends to equalize, and therefore minimize, the stress concentrations.
It is also an object of this invention to provide a new and improved slide block breech mechanism which embodies a multi-lug configuration wherein only a portion of each lug is inserted into and physically contacts a bearing surface of the mating thread, or lug, of the breech ring.
Another object of this invention is to provide a new and improved slide block breech mechanism wherein the slide block and breech ring includes a plurality of pairs of integral lugs wherein the configuration of each lug in each pair is the same, but of different configuration than each of the other pairs of lugs.
A further object of this invention is to provide a new and improved slide block breech mechanism wherein the bearing surfaces of at least one pair of breech block lugs is not initially in an abutting contact relationship with their mating ring bearing surfaces. These bearing surfaces contact under loading and deformation of the structure in such a manner as to cause a favorable stress distribution.
A still further object of this invention is to provide a new and improved slide block breech mechanism embodying a multi-lug slide block having integral means for tying together the rear portions of the two sides of the breech ring.
Other objects of this invention will, in part, be obvious and will, in part, appear hereinafter.